First of all, please ensure that you are using the latest version of Showkase (v1.3.4) to ensure that any bugs that were present in previous versions but which have since been fixed are not contributing to your problem.
If necessary, please see the Upgrading Showkase support page for details.
I have just checked that changing the 'Gallery text color' and updating a caption takes effect after clicking 'Update' and 'Publish' and everything seems to be working as expected in my own test Showkase v1.3.4 installation.
After making changes to your Showkase site, try completely clearing your browser's cache before reloading your gallery page to see if this makes a difference.
Your web server may also be caching pages which might introduce a delay before you see the updates that you make to your Showkase site.
If your web server uses Apache, try adding the following line of code to the .htaccess file in your root directory to disable server-side caching.
Header set Cache-Control "max-age=0, private, no-cache, no-store, must-revalidate"
Hopefully ensuring that you are using Showkase v1.3.4, clearing your browser's cache and disabling server-side caching will solve your problem.